﻿var countNumbersWithUniqueDigits = function (n) {
    if (n == 0) {
        return 1;
    }

    if (n == 1) {
        return 10;
    };

    let res = 10, cur = 9;
    for (let i = 0; i < n - 1; i++) {
        cur *= 9 - i;
        res += cur;
    };
    return res;
};
